In semiconductor manufacturing technology, the critical dimension (CD) of a mask or wafer are becoming continually smaller, for example, from 45 nm to 32 nm. It is important that the uniformity of the CD for various patterns, referred to as CD uniformity, remains at acceptable levels. Certain types of patterns require different levels of CD uniformity. For example, isolated lines as used in a microprocessor circuit may require a CD uniformity of 1.3 nm, 3 sigma for a 45 nm process, and dense lines as used in memory arrays may require a CD uniformity of 3.4 nm, 3 sigma.
The proximity of isolated/dense (iso-dense) patterns also becomes more difficult to control. While CD uniformity of the iso-dense patterns may be compensated based on the exposure dosage, a need exists for a method and system that better predicts the proximity of iso-dense patterns on a mask or wafer to improve CD uniformity of the mask or wafer.